JP6413987B2 - Radio wave arrival direction estimation device, radio wave arrival direction estimation system - Google Patents

Description

  The present invention relates to a radio wave arrival direction estimation device that estimates from which direction a radio wave emitted by a wireless tag comes, and a radio wave arrival direction estimation system including the device and a wireless tag.

  The Pseudo-doppler method is known as one of the methods for estimating the radio wave arrival direction (for example, Non-Patent Document 1). In the Pseudo-doppler method, an antenna is mounted on a rotating plate or the like, and the antenna is moved to create a Doppler shift for radio waves emitted from a radio wave source. Since the signal received by the antenna changes due to the created Doppler shift, the change of the signal is analyzed to estimate the direction of the radio wave source. In Non-Patent Document 1, Fourier transform is used for analysis of a signal received by an antenna.

Chang, H.-L., Tian, J.-B., Lai, T.-T., Chu, H.-H., and Huang, P., Spinning beacons for precise indoor localization, to appear in ACM Sensys '08.

  In order to use the Pseudo-doppler method, when a device with an antenna fixed to a moving body such as a turntable (hereinafter referred to as an antenna rotating device) is installed indoors, the direct wave and the reflected wave caused by multipath may be separated. I need it.

  The direct wave and the reflected wave generated by multipath have different radio wave arrival angles. That is, the direction of the radio wave source is apparently different between the direct wave and the reflected wave. A radio wave received by a moving antenna undergoes a Doppler shift reflecting the direction of the radio wave source. Therefore, the direct wave and the reflected wave can be separated by increasing the frequency resolution.

  In the Fourier transform, the frequency resolution Δf is given by the reciprocal of the window width. That is, if the window width to be analyzed is widened, the frequency resolution is high (Δf is small), and conversely if the window width is narrowed, the frequency resolution is low (Δf is large).

  Of course, the greater the frequency difference between the direct wave and the reflected wave, the easier the separation of the direct wave and the reflected wave. Therefore, it is necessary to increase the Doppler shift amount.

  For these reasons, the apparatus described in Non-Patent Document 1 rotates a large disk with a slow rotation cycle. In the case of rotational movement, even if the rotation period is slow, if the disk is large, the speed of the antenna installed near the outer periphery of the disk increases, so the Doppler shift increases. Further, since the rotation period is slow, the time window can be widened. Therefore, the frequency resolution Δf can be increased.

  However, since a large disk is used, it cannot be easily installed in various indoor places. In order to be easily installed in various indoor places, it is desired to be small.

  To increase the Doppler shift while reducing the size of the disk, the angular velocity should be increased. However, if the angular velocity is increased, the frequency analysis window cannot be widened. This is because the time window T has a relationship of T = N / fs (N is the number of sampling points, fs is the sampling frequency), and N is reduced when the angular velocity is increased. If the angular velocity is increased, the frequency analysis window cannot be widened, so that the frequency resolution is lowered.

  Instead of frequency analysis by Fourier transform, prepare a measurement signal model and change the parameter of the model, and use a method to determine the degree of coincidence with the measurement signal. Thus, the angular resolution can be increased.

  However, the distance between the antenna and the wireless tag changes continuously due to the movement of the antenna, and the model of the measurement signal representing the Doppler shift caused by this change in distance becomes a complicated model if expressed strictly. As a result, the amount of calculation increases. If the model is simplified using approximation, the amount of calculation is reduced, but if the approximation is not appropriate, the estimation accuracy of the radio wave arrival direction is lowered.

  The present invention has been made based on this circumstance, and the object of the present invention is the direction of arrival of radio waves that can be downsized, have high angular resolution, high accuracy, and can reduce the amount of calculation. To provide an estimation device and a radio wave arrival direction estimation system.

  The above object is achieved by a combination of the features described in the independent claims, and the subclaims define further advantageous embodiments of the invention. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiments described later as one aspect, and do not limit the technical scope of the present invention. .

The present invention for achieving the above object is a radio wave arrival direction estimation device that estimates the arrival direction of a radio wave having a preset constant frequency transmitted by the wireless tag (300),
A reciprocating linear motion body (111, 131, 151) that reciprocates linearly, a drive unit (113, 133, 153) that moves the reciprocating linear motion body at a preset speed, and a wireless tag fixed to the reciprocating linear motion body An antenna (112, 132, 152) that receives radio waves transmitted by the receiver, and a receiving unit (100, 100A) that outputs a measurement signal that is a signal determined based on the radio waves received by the antenna;
Approximate measurement that represents a measurement signal using an approximation that uses a plane wave as the radio wave transmitted by the wireless tag, and includes an azimuth and phase that are the angle between the reference azimuth and the direction from which the radio wave arrives as an unknown parameter Direction to determine the azimuth angle in the approximate measurement signal model that best matches the measurement signal by calculating the degree of coincidence between the signal model and the measurement signal output by the receiver while changing the unknown parameter of the approximate measurement signal model And a determination unit (230, 230A).

  In the present invention, the apparatus can be downsized for the following reason. The frequency transmitted by the wireless tag is set to a constant frequency, but naturally, a certain amount of fluctuation occurs in the transmitted frequency in the actual device. If the magnitude of the Doppler shift caused by the movement of the antenna is about the same as the fluctuation range of the frequency transmitted by the wireless tag, the frequency fluctuation caused by the Doppler shift cannot be distinguished from the fluctuation of the frequency transmitted by the wireless tag. Therefore, regardless of the frequency analysis method, the Pseudo-doppler method needs to move the antenna at a speed at which a certain amount of Doppler shift occurs.

  When the antenna is moved at high speed, the window width becomes narrower. However, in the present invention, the azimuth angle in the approximate measurement signal model is determined using not the Fourier transform but the degree of coincidence between the measurement signal output from the receiving unit and the approximate measurement signal model. That is, the azimuth angle is obtained by a method that is not restricted by the window width. Therefore, the Doppler shift can be increased by moving the antenna at high speed. That is, it is not necessary to lengthen the stroke of the linear motion in order to increase the motion speed of the antenna. Therefore, the apparatus can be miniaturized. Further, in order to increase the angular resolution, it is only necessary to narrow the pitch for numerical search, so it is easy to increase the angular resolution.

  In the present invention, the azimuth angle can be accurately estimated for the following reason while reducing the amount of calculation. In the present invention, since the antenna reciprocates linearly and the distance to the wireless tag changes, a Doppler shift occurs in the radio wave received by the antenna. Therefore, the frequency of the radio wave received by the antenna varies with the movement of the antenna. . For this reason, if the radio wave received by the antenna is modeled strictly, a complicated model is generated and the amount of calculation increases.

  Therefore, the present invention uses an approximate measurement signal model that approximates the measurement signal. The radio wave transmitted by the wireless tag is actually a spherical wave, but the approximate measurement signal model in the present invention obtains the radio wave transmitted by the wireless tag by approximating it as a plane wave.

  The approximation as a plane wave is that the wireless tag is assumed to exist in the same direction with respect to the antenna regardless of the position of the antenna. As the distance from the antenna to the wireless tag is longer than the amount of movement of the antenna, the direction change of the wireless tag relative to the antenna is smaller even if the antenna moves. In the present invention, as described above, the apparatus can be miniaturized. If the device is small, the amount of movement of the antenna is small, and if the amount of movement of the antenna is small, the distance from the antenna to the wireless tag tends to be longer than the amount of movement of the antenna. Therefore, the approximation to the plane wave can estimate the direction of arrival of the radio wave with an accuracy close to that when the radio wave received by the antenna is strictly modeled in the present invention that can reduce the size of the apparatus. Since the arrival direction of radio waves can be estimated with an accuracy close to that when strictly modeled, it can be said that the approximation using a plane wave can accurately estimate the arrival direction of radio waves in the present invention in which the apparatus can be downsized.

  In addition, an approximate measurement signal model using approximation as a plane wave will be described in detail later, but there is no square root that exists when it is modeled strictly. Therefore, the amount of calculation can be greatly reduced as compared with the case of strict modeling.

In the invention according to claim 2, the receiving unit is
The reciprocating linear motion body includes a first reciprocating linear motion body (111) and a second reciprocating linear motion body (131) in which the directions of the reciprocating linear motion intersect each other,
As drive units, a first drive unit (113) that moves the first reciprocating linear motion body at a preset speed and a second drive unit (133) that moves the second reciprocating linear motion body at a preset speed are provided. ,
The antenna includes a first antenna (112) fixed to the first reciprocating linear motion body and a second antenna (132) fixed to the second reciprocating linear motion body,
The direction determining unit
The degree of coincidence between the first measurement signal, which is a measurement signal determined based on the radio wave received by the first antenna, and the approximate measurement signal model is calculated while changing unknown parameters of the approximate measurement signal model, Determining at least one set of azimuth angles in the approximate measurement signal model that most closely match, having the same absolute value and different signs,
The degree of coincidence between the second measurement signal, which is a measurement signal determined based on the radio wave received by the second antenna, and the approximate measurement signal model is calculated while changing an unknown parameter of the approximate measurement signal model. Determining at least one set of azimuth angles in the most similar approximate measurement signal model that have the same absolute value and different signs,
Of each set of azimuth angles determined using the first measurement signal, the azimuth angle indicating the same direction as the azimuth angle determined using the second measurement signal is defined as the azimuth angle from which the radio wave actually arrives. presume.

  As will be described later in detail in the approximate measurement signal model, the azimuth is an argument of the cosine function. Therefore, the azimuth angle that is the approximate measurement signal model that most closely matches the measurement signal always has the same absolute value and takes two values with different signs. Since only one of these two values is the azimuth angle from which radio waves actually arrive, determine which of these two values is the azimuth angle from which radio waves actually arrive There is a need to.

  Here, the azimuth angle in the approximate measurement signal model is an angle based on the movement direction of the reciprocating linear moving body. Accordingly, in the invention according to claim 2, as the reciprocating linear motion body, the first reciprocating linear motion body and the second reciprocating linear motion body whose directions of the reciprocating linear motion intersect each other, the first reciprocating linear motion body, A first antenna and a second antenna are respectively fixed to the two reciprocating linear motion bodies. Since the directions of the reciprocating linear motion intersect with each other, only the azimuth in which radio waves actually arrived among the azimuths of each set determined from the approximate measurement signal model that best matches the first measurement signal is the second azimuth. It represents the same direction as the azimuth angle determined from the approximate measurement signal model that most closely matches the measurement signal.

  Therefore, in the invention according to claim 2, among the azimuth angles determined from the first measurement signal, the azimuth angle indicating the same direction as the azimuth angle determined from the second measurement signal is actually transmitted by the radio wave. Estimated as the azimuth angle coming. By doing so, it is possible to estimate the azimuth angle from which radio waves actually arrive.

方向決定部は、測定信号をＶ_ｇｅｔ-、サンプリング番号をｋ、総サンプリング数をＫとしたとき、式６で表す残差ｅが最小となる複数の到来波の方位角の組み合わせを探索するものであって、

式６をＢで偏微分した式と、式６をＣで偏微分した式をそれぞれ０とすることで立式される連立方程式を解くことによりＢ、Ｃを算出し、算出したＢ、Ｃを用いて、残差ｅが最小となる複数の到来波の方位角の組み合わせを探索する。 In the invention according to claim 3, the receiving unit includes a frequency converting unit (120, 140, 160) that converts the radio wave received by the antenna into a signal having an intermediate frequency lower than the frequency of the radio wave, and the frequency is used as a measurement signal. The conversion unit outputs the signal whose frequency is converted,
The approximate measurement signal model is a model obtained by converting a composite wave of a plurality of incoming waves into an intermediate frequency signal, where the frequency of the radio wave transmitted by the wireless tag is f _RF , the intermediate frequency is f _IF , the time is t, and the speed of light is v _c , the distance from the moving center of the antenna to the antenna, x _v , the azimuth angle of each incoming wave, φ _m , the amplitude of each incoming wave, A _m , the phase of each incoming wave, Ψ _m , and the number of incoming waves N, when the approximate measurement signal model is V _ref , it is a model represented by Equation 1 or Equation 2, Equation 3, Equation 4, and Equation 5,

The direction determining unit searches for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e expressed by Equation 6 where V _get− is the measurement signal, k is the sampling number, and K is the total number of samplings. Because

B and C are calculated by solving simultaneous equations formed by partial differentiation of Equation 6 by B and partial differentiation of Equation 6 by C to 0, and calculating the calculated B and C. And search for a combination of azimuth angles of a plurality of incoming waves with the smallest residual e.

The invention according to the claims 3, B by simultaneous equations, it is possible to calculate the C, the unknown parameter is only the azimuth angle phi _m in formula 6. Therefore, the unknown parameters that need to be searched are only combinations of the azimuth angle φ _m , and the unknown parameters to be searched are reduced, so that the calculation can be performed quickly.

In the invention according to claim 4, the direction determining unit removes the term of only the measurement signal from Equation 6 and calculates a plurality of incoming waves having the maximum residual energy E calculated by Equation 7 with the sign inverted. By searching for a combination of azimuth angles, a search is made for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e expressed by Equation 6.

  In this way, it is possible to search for a combination of azimuth angles of a plurality of arriving waves that minimize the residual e, without calculating the term of only the measurement signal, thereby reducing the amount of calculation. In addition, even if the term of only the measurement signal is removed from Equation 6, the equation obtained by partial differentiation with B and C does not change. Therefore, even when Expression 7 is used, the simultaneous equations for calculating B and C are the same as when Expression 6 is used.

方向決定部は、記憶部に記憶されているｚ因子項の計算値を用いて、複数の方位角、時刻に対する式８、式９の値を算出する。 The invention according to claim 5 inputs a plurality of azimuth angles and times into a z-factor term that can calculate a value by determining z in equations 8 and 9, which are part of the equation for calculating the residual e. A storage unit (220) that stores the calculated value of the z-factor term calculated in

The direction determination unit calculates the values of Equations 8 and 9 for a plurality of azimuth angles and times using the calculated value of the z-factor term stored in the storage unit.

  In this way, by calculating Equation 8 and Equation 9 for a plurality of azimuth angles and times using the calculated value of the z-factor term calculated in advance, the amount of calculation when estimating the azimuth angle is reduced. It can be estimated quickly.

In the invention which concerns on Claim 6, a receiving part is:
The reciprocating linear motion body includes a first reciprocating linear motion body (111) and a second reciprocating linear motion body (131) whose directions of reciprocating linear motion intersect each other on the same plane,
As drive units, a first drive unit (113) that moves the first reciprocating linear motion body at a preset speed and a second drive unit (133) that moves the second reciprocating linear motion body at a preset speed are provided. ,
The antenna includes a first antenna (112) fixed to the first reciprocating linear motion body and a second antenna (132) fixed to the second reciprocating linear motion body,
The approximate measurement signal model includes, as unknown parameters, in addition to the azimuth and phase, the elevation angle of the traveling direction of the radio wave with respect to the plane including the moving direction of the reciprocating linear moving body,
The direction determining unit
This is a measurement signal that is determined based on a combined angle approximate model that is a model obtained by changing the azimuth angle and elevation angle in the approximate measurement signal model to a composite angle that is a combination of the azimuth angle and the elevation angle, and the radio wave received by the first antenna. The degree of coincidence with the first measurement signal is calculated while changing unknown parameters of the synthetic angle approximation model, and the synthetic angle in the synthetic angle approximation model that most closely matches the first measurement signal is determined.
The degree of coincidence between the synthesized angle approximation model and the second measurement signal, which is a measurement signal determined based on the radio wave received by the second antenna, is calculated while changing the unknown parameter of the synthesized angle approximation model. Determine the composite angle in the matching composite angle approximation model,
An azimuth angle and an elevation angle are determined based on the composite angle determined using the first measurement signal and the composite angle determined using the second measurement signal.

  According to the present invention, the approximate measurement signal model also includes the elevation angle as an unknown parameter. Even if this approximate measurement signal model is used as it is and the degree of coincidence with the measurement signal is calculated, a large number of azimuth and elevation angle solutions where the approximate measurement signal model and the measurement signal most closely match are obtained. It is difficult to estimate.

  However, the present invention uses a synthesized angle approximation model in which the azimuth angle and elevation angle in the approximate measurement signal model are changed to a synthesized angle obtained by synthesizing the azimuth angle and elevation angle. The direction determining unit determines a composite angle at which the composite angle approximate model most closely matches the first measurement signal and a composite angle at which the composite angle approximate model most closely matches the second measurement signal.

  By combining the two angles, the azimuth angle and the elevation angle, as a composite angle, the composite angle that the composite angle approximation model best matches the first measurement signal and the composite angle that the composite angle approximation model best matches the second measurement signal are , Each can be determined as one. Further, since two composite angles are obtained, the azimuth angle and the elevation angle can be estimated from the relationship between these two composite angles, the azimuth angle and the elevation angle, and the composite angle.

In the invention according to claim 7, the receiving unit further includes:
A third reciprocating linear motion body (151) that reciprocates linearly in a direction perpendicular to a plane in which the first reciprocating linear motion body and the second reciprocating linear motion body move;
A third drive unit (153) for moving the third reciprocating linear moving body at a preset speed;
A third antenna (152) fixed to the third reciprocating linear motion body;
The direction determining unit (230A)
In addition to calculating the degree of coincidence between the first measurement signal and the synthesized angle approximation model, and the degree of coincidence between the second measurement signal and the synthesized angle approximation model, based on the radio wave received by the synthesized angle approximation model and the third antenna The degree of coincidence with the third measurement signal that is the determined measurement signal is calculated while changing the unknown parameter of the synthetic angle approximation model, and the synthetic angle in the synthetic angle approximation model that most closely matches the third measurement signal is determined,
Based on the composite angle determined using the first measurement signal and the composite angle determined using the second measurement signal, two elevation angles having the same absolute value and different signs are determined,
Based on the composite angle determined using one of the first measurement signal and the second measurement signal and the composite angle determined using the third measurement signal, two elevation angles having the same absolute value but different signs are obtained. Decide
Of the two elevation angles determined from the combined angle determined using the first measurement signal and the combined angle determined using the second measurement signal, the determination is made using either the first measurement signal or the second measurement signal. The elevation angle determined from the synthesized angle and the synthesized angle determined using the third measurement signal is estimated as the elevation angle at which the radio wave actually arrives.

  When only the composite angle determined from the first measurement signal and the second measurement signal is used, two values having the same absolute value but different signs are obtained as the elevation angle. For example, when the radio wave arrival direction estimation device is installed on the floor or ceiling, depending on the installation position of the radio wave arrival direction estimation device, one of two values having the same absolute value obtained as the elevation angle and different signs can be excluded. The elevation angle can be determined as one value only by the composite angle determined from the first measurement signal and the second measurement signal.

  However, the present invention includes the third reciprocating linear moving body. The third reciprocating linear moving body reciprocates linearly in a direction intersecting the plane in which the first reciprocating linear moving body and the second reciprocating linear moving body move, and the third antenna is connected to the third reciprocating linear moving body. It is fixed and reciprocates linearly. Therefore, the direction in which the combined angle determined from the third measurement signal determined based on the radio wave received by the third antenna is 0 degrees is different from the combined angle determined from the first measurement signal and the second measurement signal. Therefore, by using the composite angle determined from the third measurement signal, one of two elevation angle values having the same absolute value but different signs determined from the first measurement signal and the second measurement signal can be excluded.

  Thus, in the present invention, since the elevation angle can be determined as one by contrasting the elevation angle, even if the radio wave arrival direction estimation device is installed at a position where the elevation angle of the radio wave arrival direction can have a positive or negative value, the radio wave arrival direction Can be determined as a single value.

  The invention according to claim 8 is a radio wave arrival direction estimation system including the radio wave arrival direction estimation device according to any one of claims 1 to 7 and a wireless tag.

1 is a configuration diagram of a wireless tag reader 1. FIG. 6 is a diagram illustrating a relative position between the first antenna 112 and the wireless tag 300. FIG. It is a figure explaining plane wave approximation. It is a figure explaining that the azimuth angle (phi) can be determined to one by using the two antennas 112 and 132. FIG. It is a figure which shows the positional relationship of the wireless tag 300 and the 1st antenna 112 in three dimensions. It is a diagram illustrating the s-axis component of the movement amount X _V of the first antenna 112. It is a figure explaining the moving amount | distance of the 1st antenna 112 in zs plane. It is a figure explaining synthetic | combination angle | corner (gamma). It is a figure which shows the presence range of the wireless tag 300 specified by the synthetic | combination angle | corner (gamma). It is a figure explaining narrowing down azimuth angle (phi) by calculating two synthetic angles (gamma) ₁ and (gamma) ₂ . It is a block diagram of the wireless tag reader 2 of 3rd Embodiment.

<First Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The radio wave arrival direction estimation system according to this embodiment includes the wireless tag reader 1 and the wireless tag 300 shown in FIG. The wireless tag reader 1 is an example of a radio wave arrival direction estimating device.

RFID tag 300 transmits an unmodulated wave having a constant carrier frequency f _RF that is set in advance. The wireless tag 300 is of an active type and may transmit radio waves continuously, but it is preferable to transmit radio waves intermittently from the viewpoint of battery life. The wireless tag 300 is carried by a person and has a size that can be easily accommodated in a pocket of clothes.

  The wireless tag reader 1 includes a receiving unit 100 and a signal processing unit 200, and the receiving unit 100 includes a first antenna unit 110, a second antenna unit 130, a first frequency conversion unit 120, and a second frequency conversion unit 140. .

[Description of First Antenna Unit 110]
The first antenna unit 110 includes a first reciprocating linear moving body 111, a first antenna 112, and a first drive unit 113. The first reciprocating linear motion body 111 is a moving body that reciprocates linearly in a predetermined range in both directions of the straight line. As the first reciprocating linear motion body 111, various known mechanisms that perform reciprocating linear motion such as a reciprocating slider mechanism can be used. The first reciprocating linear motion body 111 is installed on a predetermined installation surface such as the ground, and moves in parallel to the installation surface. The first reciprocating linear moving body 111 has a length in the range of 10 centimeters to several tens of centimeters.

  The first antenna 112 of the present embodiment is a rod-shaped antenna and is fixed to the first reciprocating linear motion body 111. The first antenna 112 is fixed to the first reciprocating linear motion body 111 so as to be orthogonal to the installation surface, and the first reciprocating linear motion body 111 reciprocates linearly within a predetermined range.

  The 1st drive part 113 is the structure provided with the motor, and makes the 1st reciprocating linear motion body 111 reciprocating linearly move at a fixed speed. The speed at which the first reciprocating linear moving body 111 is moved is determined in advance based on the Doppler shift to be secured.

[Description of First Frequency Conversion Unit 120]
The first frequency conversion unit 120 includes a low noise amplifier 121, an RF / IF unit 122, and an AD converter (hereinafter referred to as ADC) 123. The low noise amplifier 121 is a known low noise amplifier, and amplifies a weak radio wave received by the first antenna 112 while reducing the addition of noise and sends the amplified radio wave to the RF / IF unit 122.

  The RF / IF unit 122 converts the input high frequency signal into a signal having a predetermined intermediate frequency. For example, a signal generated by a local oscillator and an input high-frequency signal are mixed to convert it to an intermediate frequency signal. Then, the frequency-converted signal is sent to the ADC 123. The ADC 123 converts the input analog signal into a digital signal and sends it to the signal processing unit 200.

[Description of Second Antenna Unit 130]
The second antenna unit 130 is disposed close to the first antenna unit 110 and includes a second reciprocating linear motion body 131, a second antenna 132, and a second drive unit 133. The second reciprocating linear moving body 131, the second antenna 132, and the second driving unit 133 are respectively the first reciprocating linear moving body 111, the first antenna 112, and the first driving unit 113 included in the first antenna unit 110. It is the same configuration.

  However, the direction of the reciprocating linear motion of the second reciprocating linear motion body 131 is different from the direction of the reciprocating linear motion of the first reciprocating linear motion body 111. Specifically, the direction of the reciprocating linear motion of the second reciprocating linear motion body 131 is on the same plane as the first reciprocating linear motion body 111, but is orthogonal to the direction in which the first reciprocating linear motion body 111 moves linearly. It is in the direction. If the direction in which the second reciprocating linear motion body 131 linearly moves and the direction in which the first reciprocating linear motion body 111 linearly moves are not parallel, the arrangement direction of the second reciprocating linear motion body 131 is the first reciprocating motion. The direction need not be orthogonal to the linear motion body 111.

[Description of Frequency Conversion Unit 140]
The frequency conversion unit 140 includes a low noise amplifier 121, an RF / IF unit 142, and an ADC 143 having the same configuration as the low noise amplifier 121, the RF / IF unit 122, and the ADC 123 included in the first frequency conversion unit 120.

[Description of Signal Processing Unit 200]
The signal processing unit 200 includes a signal acquisition unit 210, a storage unit 220, and a direction determination unit 230. The signal acquisition unit 210 acquires signals from the ADCs 123 and 143 and stores the acquired signals in the storage unit 220 or a predetermined storage unit such as a RAM (not shown). The signal signal acquisition unit 210 has acquired from ADC 123, hereinafter, as a first measurement signal _{V get1,} signal acquisition unit 210 is a signal obtained from ADC143, and the second measurement signal _{V get2.} Also, the first measurement signal _{V get1,} when not distinguished second measurement signal _{V Get2} is simply a measurement signal _{V The get.}

The wireless tag 300 transmits an unmodulated wave. However, the distance between the antennas 112 and 132 with respect to the wireless tag 300 changes as the reciprocating linear motion members 111 and 131 reciprocate linearly. Therefore, the frequency of the radio wave received by the antennas 112 and 132 varies. Therefore, the frequency of the measurement signal V _get also varies.

The storage unit 220 stores an approximate measurement signal model that is an expression representing the measurement signal V _get using an approximation in which a radio wave transmitted by the wireless tag 300 is a plane wave. More specifically, the approximate measurement signal model is a model shown in Equation 19 described later. Further, the storage unit 220 also stores calculation values calculated in advance by changing the time t and the azimuth angle φ for the coefficient S shown in cosz, sinz, and Expression 26 described later.

[Explanation of approximate measurement signal model]
This approximate measurement signal model will be described using an example in which the first antenna 112 is an antenna that receives radio waves from the wireless tag 300. Even if the antenna that receives radio waves from the wireless tag 300 is the second antenna 132, the approximate measurement signal model is the same.

  FIG. 2 shows a relative position between the first antenna 112 and the wireless tag 300. Note that FIG. 2 assumes that the wireless tag 300 is on a plane (hereinafter referred to as an antenna installation surface) on which the first reciprocating linear moving body 111 moves. The first antenna 112 is installed perpendicular to the antenna installation surface.

When points on the antenna installation surface are represented by x and y, FIG. 2 represents the x and y coordinates of the wireless tag 300. As shown in FIG. 2, in the following description, it is assumed that the radio wave transmitted by the wireless tag 300 has a frequency of f _RF , an amplitude of A, and a phase of Ψ _T. Also, the movement center point of the first antenna 112 is the origin of the antenna installation surface, the movement direction of the first antenna 112 is the x direction, and the direction on the installation surface and orthogonal to the movement direction of the first antenna 112 is the y direction. To do. Further, the movement amount of the first antenna 112 is x _V , and the angle between the line segment connecting the origin O and the wireless tag 300 and the x axis is the azimuth angle φ. When the azimuth angle φ is defined in this way, the direction from the origin O toward the positive direction of the x axis is the reference azimuth. The distance between the wireless tag 300 and the origin is L 2 _O.

When these symbols are used, the distance between the wireless tag 300 and the first antenna 112 can be expressed by Equation 10 below.

Further, when Expression 10 is used, a signal representing the radio wave from the wireless tag 300 received by the first antenna 112 (hereinafter, a received signal) can be expressed by Expression 11. In Expression 11, A is the amplitude of the received waveform, _{v c} is the speed of light, t is the measured time.

Since the frequency of radio waves is high because it radiates into the air, sampling is usually difficult as it is. Therefore, the frequency is lowered by mixing with the local signal. Frequency _{f LO,} the mixing with the signal of the phase [psi _LO, the received signal _{V R} after mixing the formula 12.

The model represented by Expression 12 is a model that does not use approximation. Hereinafter, the model represented by Expression 12 is referred to as an exact model. The L _R due to the first antenna 112 is linearly reciprocated increased or decreased, varying the phase of the received waveform by increasing or decreasing the L _R. Therefore, the frequency of the received signal V _R after mixing varies with time. Therefore, in the Fourier transform methods require a certain amount of window width to do good analysis accuracy can not be analyzed accurately received signal V _R after mixing.

Therefore, in this embodiment, the azimuth angle φ is estimated by model matching. However, exact model shown in Equation 12, the wireless tag 300 includes a distance L _R between the first antenna 112, the distance L _R, as shown in Equation 1, the entire expression within the square root is there. Therefore, using the exact model of Equation 12 requires complex calculations. Therefore, in this embodiment, in order to simplify the calculation, an approximate measurement signal model that approximates the radio wave transmitted by the wireless tag 300 as a plane wave and approximates the exact model shown in Expression 12 is used.

  Considering that the radio wave transmitted by the wireless tag 300 is a plane wave, the radio wave received by the first antenna 112 is the origin that is the movement center point of the first antenna 112 from the wireless tag 300 regardless of the position of the first antenna 112. It can be considered that it is parallel to the radio wave toward O.

In this case, as shown in FIG. 3, the radio wave reaches the first antenna 112, the approximate wave source 300a over from the radio tag 300 line vertical L _T against radio waves to the origin O of the first antenna 112 Can be regarded as being sent from.

3 that the approximate distance L _R ′ from the approximate radio wave source 300a to the first antenna 112 can be expressed by Equation 13.

The approximate distance L _R ′ shown in Equation 13 is used instead of _LR . That is, the approximate distance L _R ′ is substituted for the distance L _R in Equation 12. L _O is a fixed value when the wireless tag 300 is not moving, and f _RF is also a fixed value if there is no variation in the frequency at which the wireless tag 300 oscillates. Therefore, these L 2 _O and f _RF are also summarized as the phase Ψ. This yields Equation 14. Equation 14 corresponds to an approximate measurement signal model. Since the expression 14 has a simple shape with no square root, the matching process is facilitated.

  In Equation 14, the unknown parameters are amplitude A, azimuth angle φ, and phase Ψ. What is necessary is just to perform a matching process by setting the combination of these three unknown parameters. However, Formula 14 is a model for a single wave. It is also necessary to analyze when radio waves arrive from multiple directions, such as in a multipath.

  Therefore, in the present embodiment, the equation is modified so that the matching process can be performed only by the combination of the arrival directions of N radio waves, that is, the combination of N azimuth angles φ.

A model expressing the measurement signal V _get when N arriving waves arrive at the first antenna 112 using Expression 14 is expressed by Expression 15.

  Equation 15 is an approximate measurement signal model for N incoming waves. However, in the present embodiment, the expression 15 is not used as it is, but is replaced with characters in order to facilitate calculation.

For later equation transformation, a part of equation 15 is replaced with a variable z shown in equation 16, and amplitude A and phase Ψ are converted into variable B _m and variable C _m shown in equation 17.

Using Expression 16, the braces in Expression 15 are represented as the left side of Expression 18. The left side of Expression 18 can be expressed as the second line of Expression 18 by using the addition theorem and the variables B _m and C _m shown in Expression 17.

When Expression 18 is used, a model (hereinafter referred to as a matching model) expressing N incoming waves is expressed by Expression 19. The matching model represented by Expression 19 is an example of the approximate measurement signal model used in this embodiment.

A residual e shown in Expression 20 is considered as an evaluation index for evaluating the degree of coincidence between the model shown in Expression 19 and the measurement signal _Vget . In Equation 20, k is a sampling number and K is the total number of samplings.

The matching model with the smallest residual e best represents the incoming wave. By replacing the expression, the matching model is expressed by Expression 19. In the matching model shown in Expression 19, unknown parameters are φ _m , B _m , and C _m .

Here, consider obtaining B _m and C _m . When the residual e is partially differentiated with respect to B _n and C _n of the n-th incoming wave, Expressions 21 and 22 are obtained.

From Equation 19, Equation 23 is obtained.

When Expression 23 and Expression 19 are applied after expanding the curly brackets in Expression 21 and Expression 22, Expression 24 and Expression 25 are obtained.

In order to simplify Expression 24 and Expression 25 by character replacement, consider the following variables shown in Expression 26.

Rewriting Expressions 24 and 25 using the variables shown in Expression 26 yields Expressions 27 and 28.

Since we want to find B _m and C _m that minimize the residual e, consider Equation 29. From Expression 29, an expression in which the left side of Expression 27 and Expression 28 is 0 is considered. Therefore, 2N simultaneous equations are obtained for each n (n = 1 to N).

When azimuth angles φ _m and φ _n are applied, z _m and z _n are obtained. Therefore, when azimuth angles φ _m and φ _n are applied, the simultaneous equations of Equation 29 are related to unknown parameters B _m and C _m for each n. 2N bottles are obtained. Therefore, if the azimuth angles φ _m and φ _n are applied, the simultaneous parameters can be solved and the unknown parameters B _m and C _m can be calculated. Further, since the residual e is the square of the difference between the measurement signal V _get and the matching model V _ref as shown in Equation 20, the residual e is a quadratic form that is convex downward with respect to B _m and C _m. It is. Therefore, by solving the simultaneous equations of Equation 29, B _m and C _m that minimize the residual e can be obtained for each azimuth angle φ _m .

Since Expression 30 is obtained from Expression 17, when B _m and C _m are obtained, the amplitude A _m and the phase Ψ _m can also be determined.

Therefore, only by searching the combination of azimuth phi _m, it can determine the matching model residuals e is minimized.

Further, in the present embodiment, the following equation modification is performed on Equation 20. When Expression 20 is expanded, Expression 31 is obtained.

The second term on the right side of Equation 31 can be transformed as Equation 32 using Equation 19 and Equation 26.

The third term on the right side of Equation 31 can be transformed as Equation 33 using Equation 19 and Equation 26.

The residual e may be obtained by directly calculating Equation 31. However, since the first term on the right side of Equation 31 is the square term of the measurement signal V _get , it is always a positive number and is not affected by the value of the azimuth angle φ _{m to be} searched. Therefore, consider the residual energy E in which the first term on the right side of Equation 31 is omitted. Residual energy E is expressed by Equation 34. The right side of Expression 34 is an expression obtained by omitting the first term and inverting the sign from the right side of Expression 31.

  In the present embodiment, the residual energy E corresponds to the degree of coincidence of claims, and the storage unit 220 stores Expression 34. Since the first term on the right side of Expression 34 is expressed by Expression 32 and the second term is expressed by Expression 33, Expression 32 and Expression 33 are also stored in the storage unit 220.

In Expressions 32 and 33, the coefficient indicated by S has only z as a variable. D is also a variable having a variable z. In this variable z, since the movement amount x _V is a function of time t, the variable z is the time t, can be calculated in advance be determined azimuth angle phi _m.

In this embodiment, the time t and the azimuth angle φ _m are changed in various _ways , and the cos value and sin value of the variable z calculated in advance, and the coefficients S _BCnm and S _BSnm that can be calculated from the cos value and sin value of the variable z. The calculated values of S _CCnm and S _CSnm are also stored in the storage unit 220.

More specifically, the azimuth angle φ _m is changed at an angular pitch determined based on the angular resolution, and for each azimuth angle φ _m , the time t is set for each predetermined time pitch over the time length of the waveform to be matched. The cos value and sin value of the variable z when changed are stored in the storage unit 220. The predetermined time pitch is the same as the sampling period, for example. The coefficient S that can be calculated from the cos value and sin value of the variable z is also stored in the storage unit 220. _{cosz, sinz, S BCnm, S} BSnm, S CCnm, S CSnm corresponds to the z factor preceding claims.

The direction determining unit 230 performs the following calculation to estimate the azimuth angle φ _m from which the radio wave from the wireless tag 300 arrives.

(A) (A1) to (A5) are performed on the measurement signals V _get acquired from the ADCs 123 and 143, respectively.

(A1) The measurement signal V _get is acquired, and the calculated values of cosz _n and sinz _n stored in the storage unit 220 for each φ _m included in the combination of the measurement signal V _get and the azimuth angle φ _m Then, D _Bn and D _Cn in Equation 26 are calculated for each φ _m .

(A2) thereof _{D Bn,} based on the _{D Cn,} the simultaneous equation of Equation 29 by solving for each phi _m, obtaining _B m, the _{C m} for each phi _m.

(A3) Substituting the B _m , C _m , the previously obtained D _Bn , D _Cn , and the calculated value of the coefficient S stored in the storage unit 220 into the expressions 32 and 33, the first term in By calculating the second term and adding them, the residual energy E is calculated for each combination of φ _m .

(A4) Among the residual energies E obtained for each combination of φ _m , the maximum residual energy E is determined.

(A5) The combination of φ _{m that has} the maximum residual energy E is determined. As shown in Expression 14, since φ is an argument of cos, the combination of φ _m that has the maximum residual energy E has two values having the same absolute value but different signs. . This is expressed as ± φ _m . It is impossible to determine which sign of φ _m is correct from only one measurement signal V _get . Therefore, two φ _m having the same absolute value and different signs are set as candidates for the azimuth angle φ _m .

Here, the moving direction of the first antenna 112 is taken as the x1 axis, and the moving direction of the second antenna 132 is taken as the x2 axis. Further, the .phi.2 _m the azimuth angle phi _m calculated using .phi.1 _m, the second measurement signal _{V Get2} the azimuth angle phi _m calculated using the first measurement signal _{V get1.} Note that φ1 _m has the x1 axis as the reference orientation, and φ2 _m has the x2 axis as the reference orientation.

The first measurement signal _{V get1,} the second measurement signal _{V get2,} by implementing each (A1) ~ (A5), ± φ1 m, ± φ2 m is obtained.

In the example of FIG. 4, ₁ candidate determined using the first measurement signal _{V get1} is phi, it is -.phi _{1, 2} candidate determined using the second measurement signal _{V Get2} is phi, is -.phi _2.

Of the candidates ± φ _{m for} the azimuth angle φ _m , only one is the azimuth angle φ _{m from} which radio waves actually arrive. The other will be called a ghost. When the directions in which the two reciprocating linear motion bodies 111 and 131 linearly move are not parallel, the azimuth angle φ _m from which radio waves actually arrive is either φ ₂ or −φ ₂ of φ ₁ and −φ _1. The ghost does not overlap with the other candidate.

(B) Therefore, by executing A, the azimuth angle φ1 representing the same direction as ± φ2 _m for each set of ± φ1 _m1 obtained from the first measurement signal V _get1 and having the same absolute value and different signs Determine _m . The determined azimuth angle .phi.1 _m, actually the azimuth .phi.1 _m radio waves are coming.

In the example of FIG. 4, φ ₁ represents the same direction as φ ₂ . Meanwhile, -.phi ₁ is, phi ₂ both not also represent the same direction as the -.phi _2. Therefore, let φ1 be the azimuth angle from which the radio wave actually arrives.

The process B is performed for each m. Therefore, if m is 2 or more, a plurality of azimuth angles φ _m can be determined. Among these plural φ _m , any one is a direct wave, and the remaining is an indirect wave caused by multipath. For example, each determined amplitude A from a plurality of azimuth angles phi _m, and azimuth angle phi _m of the direct wave of the azimuth angle phi _m corresponding to the maximum amplitude A.

[Summary of First Embodiment]
As described above, in the present embodiment described above, the wireless tag reader 1 can be downsized. The reason is as follows. As already described, in the Pseudo-doppler method, it is necessary to move the antennas 112 and 132 at a speed at which a certain amount of Doppler shift occurs.

When the antennas 112 and 132 are moved at high speed, the window width is narrowed. However, in this embodiment, not the Fourier transform but the residual energy E representing the degree of coincidence between the measurement signal V _get and the approximate measurement signal model is calculated, and the azimuth angle φ in the approximate measurement signal model is determined. That is, the azimuth angle φ is obtained by a method that is not restricted by the window width. Therefore, the Doppler shift can be increased by moving the antennas 112 and 132 at high speed. That is, it is not necessary to increase the stroke of the linear motion of the antennas 112 and 132 in order to increase the motion speed of the antennas 112 and 132. Therefore, the wireless tag reader 1 can be downsized. Further, in order to increase the angular resolution, it is only necessary to narrow the pitch for numerical search, so it is easy to increase the angular resolution.

  In the present embodiment, the azimuth angle φ can be accurately estimated for the following reason while reducing the amount of calculation. As already described, if the radio waves received by the antennas 112 and 132 are modeled strictly, a complicated model is generated and the amount of calculation increases. Therefore, in this embodiment, an approximate measurement signal model is used. The radio wave transmitted by the wireless tag 300 is actually a spherical wave, but the approximate measurement signal model approximates the radio wave transmitted by the wireless tag 300 as a plane wave.

  The approximation as a plane wave is that the wireless tag 300 is assumed to exist in the same direction with respect to the antennas 112 and 132 regardless of the positions of the antennas 112 and 132. As the distance from the antennas 112 and 132 to the wireless tag 300 is longer, the direction change of the wireless tag 300 relative to the antennas 112 and 132 is smaller as the distance from the antennas 112 and 132 to the wireless tag 300 is longer. . As already described, the wireless tag reader 1 of the present embodiment can be miniaturized. If the wireless tag reader 1 is small, the amount of movement of the antennas 112 and 132 also decreases. If the amount of movement of the antennas 112 and 132 decreases, the wireless tag reader 1 wirelessly transmits from the antennas 112 and 132 compared to the amount of movement of the antennas 112 and 132. The distance to the tag 300 tends to be long. Therefore, the approximation using the plane wave is less likely to reduce accuracy compared to the case where the radio waves received by the antennas 112 and 132 are strictly modeled in the present embodiment in which the RFID tag reader 1 can be downsized. Since there is little decrease in accuracy with respect to the case where it is strictly modeled, it can be said that approximation using a plane wave can estimate the azimuth angle φ with high accuracy when the wireless tag reader 1 can be miniaturized.

  In addition, the strict model has a square root as can be seen from Equations 12 and 10, whereas the approximate measurement signal model shown in Equation 14 has no square root. By estimating, the amount of calculation can be greatly reduced.

Further, in the present embodiment, the first reciprocating linear motion body 111 and the second reciprocating linear motion body 131, and the first reciprocating linear motion body 111 and the second reciprocating linear motion body 131 intersect with each other. A first antenna 112 and a second antenna 132, which are fixed, are provided. Of the sets of azimuth ± .phi.1 _m determined from the first measurement signal _{V get1,} the azimuth angle .phi.1 _m representing the same direction as the azimuth angle .phi.2 _m determined from the second measurement signal _{V Get2,} radio waves Estimated as the incoming azimuth angle φ1 _m . In this way, the azimuth angle φ1 _{m from} which radio waves arrive can be narrowed down to one azimuth angle φ1 _m .

In this embodiment, since B _m and C _m can be calculated by simultaneous equations, the unknown parameter that needs to be searched is only a combination of the azimuth angle φ _m . Thereby, calculation can be performed rapidly.

Further, in the present embodiment, the residual energy E shown in Expression 34 is calculated by removing the term of only the measurement signal V _get from the residual e, instead of calculating the residual e shown in Expression 20. Thereby, it is possible to search for a combination of a plurality of azimuth angles φ _m of the arriving waves that minimize the residual e without calculating a term of only the measurement signal V _get , thereby _{reducing the} amount of calculation.

Furthermore, in the present embodiment, the storage unit 220 stores the calculated values of the cos value, the sin value, and the coefficients S _BCnm , S _BSnm , S _CCnm , and S _CSnm of the variable z calculated in advance by changing the time t and the azimuth angle φ _m in various _ways . The residual energy E is calculated using this calculated value. This also reduces the amount of calculation when estimating the azimuth angle φ _m , so that the azimuth angle φ _m can be estimated quickly.

Second Embodiment
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used so far are the same as elements having the same reference numerals in the previous embodiments unless otherwise specified. Further, when only a part of the configuration is described, the above-described embodiment can be applied to the other parts of the configuration.

  The radio wave arrival direction estimation system of the second embodiment also has the configuration of FIG. However, the process which the direction determination part 230 performs differs from 1st Embodiment. The direction determining unit 230 of the first embodiment has determined only the azimuth angle φ that is the angle of the plane direction in the radio wave arrival direction, but the direction determining unit 230 of the second embodiment has the following in addition to the azimuth angle φ: The elevation angle δ is also determined. The elevation angle δ is an angle of the radio wave arrival direction with respect to the xy plane.

  In the second embodiment, it is assumed that the first antenna unit 110 and the second antenna unit 130 of the wireless tag reader 1 are arranged at positions where the elevation angle δ can be limited to either one with respect to the xy plane. The position where the elevation angle δ can be limited to either one with respect to the xy plane is, for example, a floor or a ceiling.

  In the second embodiment, a coordinate system is defined as shown in FIG. The z-axis is perpendicular to the xy plane and passes through the origin O. The coordinate axis s is an axis in a linear direction in which a plane including the wireless tag 300 and the z axis intersects the xy plane. As shown in FIG. 6, the elevation angle δ is an angle formed by a line segment connecting the wireless tag 300 and the origin O and the s axis in the sz plane. 5 and 6 are coordinate systems for the first reciprocating linear moving body 111 and the first antenna 112. FIG. Since the coordinate system for the second reciprocating linear motion body 131 and the second antenna 132 may be considered in the same manner as the coordinate system for the first reciprocating linear motion body 111 and the first antenna 112, hereinafter, the first reciprocating linear motion body 111 is used. The coordinate system for the first antenna 112 will be described.

  When the plane wave approximation is performed, it is approximated that a radio wave parallel to the radio wave arriving at the center of the reciprocating motion arrives regardless of the position of the first antenna 112. In other words, the plane wave approximation approximates the position of the first antenna 112 to a position on a straight line connecting the wireless tag 300 and the origin.

As shown in FIG. 6, s-axis component of the movement amount _{x V} of the first antenna 112 is _x v cos [phi. That is, as shown in FIG. 7, the moving amount of the first antenna 112 in the zs plane is x _v cosφ. Therefore, the movement amount of the first antenna 112 approximated on a straight line connecting the wireless tag 300 and the origin is x _v cos φ cos δ as shown in FIG. Therefore, the approximate distance L _R ′ is expressed by Expression 35.

Due to the difference between Expression 35 and Expression 13, the variable z _m is expressed by Expression 36 in the second embodiment.

In this equation 36, cos φ _m cos δ _m is a multiplication of a trigonometric function, so there are many combinations of the azimuth angle φ _m and the elevation angle δ _m that have the same value after multiplication. Therefore, a composite angle γ that combines the azimuth angle φ and the elevation angle δ is considered.

  The composite angle γ is an angle obtained by multiplying the azimuth angle φ and the elevation angle δ. As shown in FIG. 8, the moving direction of the first reciprocating linear moving body 111, that is, the x axis, and the origin O and the wireless tag 300 are connected. This is the angle between the line segment.

When this composite angle γ is used, Expression 37 is established. When Expression 37 is substituted into Expression 36, Expression 38 is obtained. The variable z in Expression 38 has the same form as z in the first embodiment. In the matching model of Expression 19, the variable z is Expression 38, which is an example of the composite angle approximation model in the claims.

  The range of the radio wave arrival direction that can be narrowed down by the composite angle γ is on a conical surface indicated by a broken line in FIG. This cone is a cone having the movement center point (that is, the origin O) of the first antenna 112 as the apex and the apex angle as 2γ. Note that the apex angle of the cone is an apex angle of a triangle formed by cutting the cone along a plane including the central axis.

Also in the second embodiment, two antennas 112 and 132 are provided, and these antennas 112 and 132 are in a relationship in which the moving directions intersect each other. When the same calculation as in the first embodiment is performed using the measurement signals V _get detected using the antennas 112 and 132, the combined angle γ can be obtained from each measurement signal V _get .

  It should be noted that the composite angle γ is also calculated from two values having the same absolute value but different signs. However, since the composite angle γ represents the angle from the cone axis to the cone surface in the cone indicating the range of the radio wave arrival direction, it can be considered as a positive value. Therefore, the value of the positive composite angle γ obtained from the calculation is set as the final composite angle γ.

Here the synthetic angle gamma gamma ₁ obtained from the first measurement signal _{V get1,} the compound angle gamma obtained from the second measurement signal _{V Get2} and gamma _2. Also, if the x axis and y axis on the first antenna 112 side are x1 axis and y1 axis, and the x axis and y axis on the second antenna 132 side are x2 axis and y2 axis, the combined angles γ ₁ and γ ₂ are , As shown in FIG. The angle α shown in FIG. 10 is an angle formed by the x1 axis and the x2 axis.

cos γ ₁ can be expressed by Equation 39. Further, since the angle α and the azimuth angle φ are on the same plane, cos γ ₂ can be expressed as in Expression 40 using the angle α.

Furthermore, using Expression 39 and Expression 40, the azimuth angle φ and the elevation angle δ can be expressed as Expression 41 and Expression 42, respectively.

  As shown in Equation 41, the azimuth angle φ is uniquely determined. On the other hand, as the elevation angle δ, two values having different signs are obtained. However, in the second embodiment, the wireless tag reader 1 is arranged at a position where the elevation angle δ in the radio wave arrival direction can be limited to either positive or negative, such as a floor or a ceiling. Therefore, the elevation angle δ having the sign determined from the arrangement among the two elevation angles δ having different signs is assumed to be the elevation angle δ representing the radio wave arrival direction.

<Third Embodiment>
FIG. 11 shows the configuration of the wireless tag reader 2 provided in the radio wave arrival direction estimation system of the third embodiment. The radio wave arrival direction estimation system according to the second embodiment includes the wireless tag reader 2 and the same wireless tag 300 as that of the first embodiment. Unlike the second embodiment, the wireless tag reader 2 does not have to be arranged at a position where the elevation angle δ can be limited to either one with respect to the xy plane.

  The wireless tag reader 2 includes a receiving unit 100A and a signal processing unit 200A. The receiving unit 100A includes the same first antenna unit 110, first frequency converting unit 120, second antenna unit 130, and second frequency converting unit 140 as in the first embodiment. In addition, the receiving unit 100A includes a third antenna unit 150 and a third frequency converting unit 160.

  The third antenna unit 150 is disposed in the vicinity of the first antenna unit 110 and the second antenna unit 130, and includes a third reciprocating linear motion body 151, a third antenna 152, and a third drive unit 153. The third reciprocating linear moving body 151, the third antenna 152, and the third driving unit 153 are respectively the first reciprocating linear moving body 111, the first antenna 112, and the first driving unit 113 included in the first antenna unit 110. It is the same configuration.

  The direction of the reciprocating linear motion of the third reciprocating linear motion body 151 is parallel to the z-axis. That is, the direction of the reciprocating linear motion of the third reciprocating linear motion body 151 is perpendicular to the plane in which the first reciprocating linear motion body 111 and the second reciprocating linear motion body 131 move.

The third frequency conversion unit 160 includes a low noise amplifier 161, an RF / IF unit 162, and an ADC 163 having the same configuration as the low noise amplifier 121, the RF / IF unit 122, and the ADC 123 included in the first frequency conversion unit 120. A signal output from the ADC 163 to the signal acquisition unit 210 is referred to as a third measurement signal V _get3 .

  The processing performed by the direction determination unit 230A included in the signal processing unit 200A is different from the previous embodiments. The direction determination unit 230A performs the same processing as the direction determination unit 230 described in the second embodiment to determine one azimuth angle φ from Expressions 41 and 42 and two elevation angles δ having different signs. .

Furthermore, the direction determining unit 230A calculates the composite angle γ ₃ also from the third measurement signal V _get3 . Since the third reciprocating linear moving body 151 reciprocates linearly in the z-axis direction, the composite angle γ ₃ is an angle formed by the z-axis shown in FIG. 10 and the radio wave arrival direction.

Furthermore, the direction determining unit 230A calculates the elevation angle δ of Expression 42 using the combined angle γ ₃ instead of any of the combined angles γ ₁ and γ ₂ of Expression 39 and Expression 40. The elevation angle δ in the equation 42 calculated using the synthesized angles γ ₁ and γ ₂ is the elevation angle δ based on the xy plane, whereas the synthesized angle γ ₁ and γ _{2 in} the equations 39 and 40 are The elevation angle δ calculated using the composite angle γ ₃ instead of either is the elevation angle δ with reference to the xz plane. Specifically, the xz plane is the x ₁ z plane when γ ₁ is used, and the x ₂ z plane when γ ₂ is used.

Only one of the two elevation angles δ calculated using the composite angles γ ₁ and γ ₂ is the two elevation angles δ calculated using the composite angle γ ₃ instead of either the composite angle γ ₁ or γ _2. Represents the same direction as. Therefore, compound angle gamma _1, the two elevation [delta] calculated using the gamma _2, the compound angle gamma ₃ Synthesis angle gamma _1, and either of the two elevation calculated using in place of any of the gamma ₂ [delta] The side representing the same direction is assumed to be an elevation angle δ at which radio waves actually arrive.

  In the third embodiment, the elevation angle δ can be determined as one by calculation. Therefore, even if the wireless tag reader 2 is installed at a position where the elevation angle δ in the radio wave arrival direction can have a positive or negative value, the elevation angle δ can be determined as one value.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned embodiment, The following modification is also contained in the technical scope of this invention, Furthermore, the summary other than the following is also included. Various modifications can be made without departing from the scope.

<Modification 1>
For example, although the residual energy E is calculated in the above-described embodiment, the residual e may be calculated instead of the residual energy E. In this case, the calculation shown in Expression 43 is performed.

<Modification 2>
In the above-described embodiment, the model indicating one incoming wave is represented by Equation 18, but cos in Equation 18 may be sin. As is well known, sin and cos are only 90 degrees out of phase with each other and have the same shape.

When cos in Expression 18 is sin, a matching model, that is, an approximate measurement signal model is expressed by Expression 44.

<Modification 3>
In the first embodiment, the receiving unit 100 may include only the first antenna unit 110 and the first frequency converting unit 120 without including the second antenna unit 130 and the second frequency converting unit 140.

In this case, it cannot be narrowed down by calculation which one of the azimuth angles ± φ _m of each set having different positive and negative is correct. However, the azimuth angle ± φ _m of each set is a symmetrical angle with respect to the movement direction of the reciprocating linear moving body 111. Accordingly, if the reciprocating linear motion body 111 is disposed along the boundary of the detection range, such as the reciprocating linear motion body 111 is disposed along the wall, each set of azimuth angles ± φ _m It is possible to determine which is the azimuth angle φ _{m from} which the radio wave actually arrives.

1: wireless tag reader 2: wireless tag reader 100: receiving unit 100A: receiving unit 110: first antenna unit 111: first reciprocating linear moving body 112: first antenna 113: first driving unit 120: first frequency converting unit 121: Low noise amplifier 122: RF / IF section 130: Second antenna section 131: Second reciprocating linear moving body 132: Second antenna 133: Second drive section 140: Second frequency conversion section 141: Low noise amplifier 142: RF / IF section 150: 3rd antenna part 151: 3rd reciprocating linear moving body 152: 3rd antenna 153: 3rd drive part 160: 3rd frequency conversion part 161: Low noise amplifier 162: RF / IF part 200: Signal processing part 200A: Signal Processing unit 210: Signal acquisition unit 220: Storage unit 230: Direction determining unit 230A: Direction determining unit 300: Wireless tag 300a: Approximate radio wave source

Claims (8)

A radio wave arrival direction estimation device for estimating the arrival direction of a predetermined frequency radio wave transmitted by the wireless tag (300),
A reciprocating linear motion body (111, 131, 151) that reciprocates linearly, a drive unit (113, 133, 153) that moves the reciprocating linear motion body at a preset speed, and a fixed reciprocating linear motion body. An antenna (112, 132, 152) that receives radio waves transmitted by the wireless tag, and a receiving unit (100, 100A) that outputs a measurement signal that is a signal determined based on the radio waves received by the antenna;
A model that represents the measurement signal using an approximation in which a radio wave transmitted by the wireless tag is a plane wave, and an unknown parameter is an azimuth angle and a phase that are an angle between a reference azimuth and a direction from which the radio wave arrives. The approximate measurement that most closely matches the measurement signal by calculating the degree of coincidence between the approximate measurement signal model including the measurement signal output from the reception unit while changing the unknown parameter of the approximate measurement signal model A radio wave arrival direction estimation device comprising: a direction determination unit (230, 230A) that determines the azimuth angle in a signal model. In claim 1,
The receiver is
The reciprocating linear motion body includes a first reciprocating linear motion body (111) and a second reciprocating linear motion body (131) whose directions of reciprocating linear motion intersect each other,
As the drive unit, a first drive unit (113) that moves the first reciprocating linear motion body at a preset speed, and a second drive unit (133) that moves the second reciprocating linear motion body at a preset speed. )
The antenna includes a first antenna (112) fixed to the first reciprocating linear motion body and a second antenna (132) fixed to the second reciprocating linear motion body,
The direction determining unit
The degree of coincidence between the first measurement signal, which is the measurement signal determined based on the radio wave received by the first antenna, and the approximate measurement signal model is calculated while changing unknown parameters of the approximate measurement signal model, Determining at least one set of the azimuth angles in the approximate measurement signal model that most closely match the first measurement signal, the absolute values of which are the same and different in sign,
The degree of coincidence between the second measurement signal, which is the measurement signal determined based on the radio wave received by the second antenna, and the approximate measurement signal model is calculated while changing unknown parameters of the approximate measurement signal model, Determining at least one set of azimuth angles in the approximate measurement signal model that most closely match a second measurement signal, having the same absolute value and different signs,
Of each set of the azimuth angles determined using the first measurement signal, radio waves actually arrive at the azimuth angle indicating the same direction as the azimuth angle determined using the second measurement signal. A radio wave arrival direction estimation apparatus, wherein the estimation is made as an azimuth angle. In claim 1,
The reception unit includes a frequency conversion unit (120, 140, 160) that converts a radio wave received by the antenna into a signal having an intermediate frequency lower than the frequency of the radio wave, and the frequency conversion unit includes the frequency conversion unit as the measurement signal. Outputs the frequency converted signal,
The approximate measurement signal model is a model obtained by converting a composite wave of a plurality of incoming waves into a signal of the intermediate frequency, where the frequency of the radio wave transmitted by the wireless tag is f _RF , the intermediate frequency is f _IF , and the time is t, the speed of light v _c , the distance from the moving center of the antenna to the antenna x _v , the azimuth angle of each incoming wave φ _m , the amplitude of each incoming wave A _m , and the phase of each incoming wave Ψ _m When the number of incoming waves is N and the approximate measurement signal model is V _ref , the model is expressed by Formula 1 or Formula 2 and Formulas 3, 4, and 5;

The direction determining unit determines a combination of the azimuth angles of the plurality of arriving waves that minimizes the residual e expressed by Equation 6, where V _get is the measurement signal, k is the sampling number, and K is the total number of samplings. To explore,

The B and C are calculated by solving the simultaneous equations formed by subtracting the expression 6 obtained by partial differentiation of the expression 6 from the B and the expression obtained by partially differentiating the expression 6 from the C by 0. The radio wave arrival direction estimation apparatus, wherein the combination of the azimuth angles of the plurality of arrival waves that minimize the residual e is searched using the B and C. In claim 3,
The direction determining unit removes the term of only the measurement signal from the equation 6 and calculates the azimuth angle of the plurality of incoming waves with the maximum residual energy E calculated by the equation 7 with the sign inverted. A radio wave arrival direction estimation device, wherein a combination is searched for to search for a combination of the azimuth angles of the plurality of incoming waves that minimize the residual e expressed by Equation (6).

In claim 3 or 4,
In the equations 8 and 9 which are part of the equation for calculating the residual e, the z factor term that can be calculated by determining the z is calculated by inputting a plurality of the azimuth angles and the time. a storage unit (220) that stores a calculated value of the z-factor term;

The direction determining unit calculates the values of Equation 8 and Equation 9 for a plurality of the azimuth angles and the time using the calculated value of the z-factor term stored in the storage unit. Radio wave arrival direction estimation device. In claim 1,
The receiver is
The reciprocating linear motion body includes a first reciprocating linear motion body (111) and a second reciprocating linear motion body (131) whose directions of reciprocating linear motion intersect each other on the same plane,
As the drive unit, a first drive unit (113) that moves the first reciprocating linear motion body at a preset speed, and a second drive unit (133) that moves the second reciprocating linear motion body at a preset speed. )
The antenna includes a first antenna (112) fixed to the first reciprocating linear motion body and a second antenna (132) fixed to the second reciprocating linear motion body,
The approximate measurement signal model includes, as the unknown parameter, the elevation angle of the traveling direction of the radio wave with respect to a plane including the moving direction of the reciprocating linear moving body in addition to the azimuth angle and the phase.
The direction determining unit
Based on a synthesized angle approximation model that is a model obtained by changing the azimuth angle and the elevation angle in the approximate measurement signal model to a synthesized angle that is a synthesized angle of the azimuth angle and the elevation angle, and a radio wave received by the first antenna. The degree of coincidence with the first measurement signal, which is the measurement signal determined in this way, is calculated while changing the unknown parameter of the synthetic angle approximation model, and the synthetic angle in the synthetic angle approximation model that most closely matches the first measurement signal As well as
The degree of coincidence between the synthetic angle approximation model and the second measurement signal, which is the measurement signal determined based on the radio wave received by the second antenna, is calculated while changing the unknown parameter of the synthetic angle approximation model, Determining the composite angle in the composite angle approximation model that most closely matches the two measurement signals;
The radio wave arrival direction, wherein the azimuth angle and the elevation angle are determined based on the composite angle determined using the first measurement signal and the composite angle determined using the second measurement signal. Estimating device. In claim 6,
The receiver further includes
A third reciprocating linear moving body (151) that reciprocates linearly in a direction perpendicular to a plane in which the first reciprocating linear moving body and the second reciprocating linear moving body move;
A third drive unit (153) for moving the third reciprocating linear moving body at a preset speed;
A third antenna (152) fixed to the third reciprocating linear motion body;
The direction determining unit (230A)
In addition to calculating the degree of coincidence between the first measurement signal and the synthetic angle approximation model and the degree of coincidence between the second measurement signal and the synthetic angle approximation model, the synthetic angle approximation model and the third antenna The degree of coincidence with the third measurement signal, which is the measurement signal determined based on the received radio wave, is calculated while changing the unknown parameter of the synthetic angle approximation model, and the synthetic angle approximation that most closely matches the third measurement signal Determining the composite angle in the model;
Based on the composite angle determined using the first measurement signal and the composite angle determined using the second measurement signal, the two elevation angles having the same absolute value and different signs are determined.
Based on the composite angle determined using one of the first measurement signal and the second measurement signal and the composite angle determined using the third measurement signal, the absolute values are the same and the signs are the same. Determine two different elevation angles,
Of the two elevation angles determined from the combined angle determined using the first measurement signal and the combined angle determined using the second measurement signal, the first measurement signal and the second measurement signal The elevation angle determined from the composite angle determined using either one and the composite angle determined using the third measurement signal is estimated as an elevation angle at which radio waves actually arrive. Radio wave arrival direction estimation device.   A radio wave arrival direction estimation system comprising the radio wave arrival direction estimation device according to claim 1 and the wireless tag.

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